Background

Congenital abnormalities of the kidney and urinary tract (ureter, urethra and bladder) are some of the commonest abnormalities identified on ultrasound during pregnancy. Antenatal hydronephrosis is seen in up to 1 in 200 pregnancies. This refers to a dilatation in the collecting system of the kidney that may be physiological, or due to obstruction or reflux. Other possible findings include kidneys that are abnormal in appearance and / or position or bladder abnormalities.

The kidneys can be identified on ultrasound from 16 weeks gestational age. The 32 week scan is thought to be the best time to identify renal and urological anomalies, however many women are not scanned at this time and only have a “booking scan” at 16-20 weeks. It should be remembered therefore that a normal antenatal scan does not rule out abnormalities of the urinary tract.

Definitions of hydronephrosis vary, and if there is any abnormality on antenatal scan it is best to scan postnatally. Parent information leaflets are available about a number of the conditions that may be found.

Other conditions that may be associated with renal anomalies include single umbilical artery, oligohydramnios, and many syndromes and chromosomal abnormalities.

Why do these children need follow up?

Some abnormalities of the urinary tract detected antenatally can resolve with time. This includes many children with vesicoureteric reflux, and PUJ obstruction. It is however, important to follow them to ensure that this has happened and to identify the small number who may require surgical intervention and also those who will eventually develop chronic kidney disease. It is increasingly recognised that up to 60% of cases of antenatal hydronephrosis will resolve in the first year of life. There is a group however, at risk of progressive renal damage and managing them prospectively may minimise this.
 

• The natural history of VUR identified antenatally is that in many cases it is likely to be low grade and is less likely to be associated with urinary tract infection. For that reason MCUs are not always performed routinely to diagnose reflux, as this diagnosis does not always change clinical management. Surgical intervention is no longer routine, and the majority of these children are managed medically. However high grade reflux can be associated with renal dysplasia (intrinsic kidney parenchymal abnormality), which requires follow up . It is thought that some of the abnormalities previously attributed to “scarring” are in fact congenital.
• PUJ obstruction may increase or resolve with time, and requires ultrasound follow up. The likelihood of requiring surgical intervention with dilatation less than 15mm is small, and for that reason, even if a PUJ type configuration is suggested on ultrasound, nuclear medicine scans are not routinely performed under 15mm.
• Abnormalities of kidney parenchyma or position are not likely to resolve, and may be associated with longer term issues such as hypertension.
• All families should be told the signs and symptoms of a urinary tract infection, and what to do if they are concerned about their child, prior to discharge.
• Prescribing prophylactic antibiotics is controversial and not universally recommended. The risk of urinary tract infection should be explained to the parents. Prophylaxis is recommended if dilatation is >15mm or if there are other complicating factors. Suggest 5mg/kg/dose once daily

Guidelines for Scanning

Any antenatally detected renal tract abnormality needs to be confirmed with postnatal imaging. Up to 5mm of renal pelvis dilatation is normal on postnatal scan.

Confirmation is ideally done after Day 4 of like, as urinary flow may not be well established before that time and significant abnormalities may not be detected. However, postnatal renal ultrasonography can be requested at any time if there is associated pulmonary hypoplasia, other anomalies, a renal mass etc. Although conditions such as single kidney will not change urinary flow, they can be associated with hydronephrosis so are ideally scanned after Day 4.

The initial postnatal scans are the responsibility of the referring professionally. They are not arranged by the renal service or outpatient clinics until the child has been seen in clinic, and this is usually at 2-3 months of age.
 

Imaging Guidelines

Some children may have recommendations from the fetal medicine panel meeting.

Significant obstruction is suggested by parenchymal thinning, dilatation >15mm. If there is radiological concern about an obstructed kidney, they should be discussed with paediatric surgery.

Antenatal Findings

Referral Guidelines

Where to Refer

• Infants from the ADHB should be referred to the renal service at Starship Hospital, Central Referrals Office, Ground Floor, Building 10, Greenlane Clinical Centre.
• Infants from WDHB should be referred to the general Paediatricians at the Rangitira Unit, Waitemata District heath Board, Private Bag 93115, Henderson
• Children from outside these DHB'S should be referred to the general Paediatricians at their own DHB

Information to include in referral for outpatient review

• Name and contact number of referrer, with address
• Results of any antenatal scans
• Results of any postnatal scans

Referrals that do not include this information will be returned.

Please ensure that the referral is sent to the DHB in which the family reside.

References